RFC 6612

Internet Engineering Task Force (IETF) G. Giaretta, Ed.
Request for Comments: 6612 Qualcomm
Category: Informational May 2012
ISSN: 2070-1721
Interactions between Proxy Mobile IPv6 (PMIPv6) and Mobile IPv6 (MIPv6):
Scenarios and Related Issues
Abstract
The use of Proxy Mobile IPv6 (PMIPv6) and Mobile IPv6 (MIPv6) in the
same network requires some care. This document discusses scenarios
where such mixed usage is appropriate and points out the need for
interaction between the two mechanisms. Solutions and
recommendations to enable these scenarios are also described.
Status of This Memo
This document is not an Internet Standards Track specification; it is
published for informational purposes.
This document is a product of the Internet Engineering Task Force
(IETF). It represents the consensus of the IETF community. It has
received public review and has been approved for publication by the
Internet Engineering Steering Group (IESG). Not all documents
approved by the IESG are a candidate for any level of Internet
Standard; see Section 2 of RFC 5741.
Information about the current status of this document, any errata,
and how to provide feedback on it may be obtained at
http://www.rfc-editor.org/info/rfc6612.
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Table of Contents
1. Introduction ....................................................22. Terminology .....................................................33. Overview of the Scenarios and Related Issues ....................43.1. Issues Related to Scenario A.1 .............................83.2. Issues Related to Scenario A.2 .............................83.3. Issues Related to Scenario B ..............................104. Analysis of Possible Solutions .................................114.1. Solutions Related to Scenario A.1 .........................114.2. Solutions Related to Scenario A.2 .........................134.2.1. Mobility from a PMIPv6 Domain to a
Non-PMIPv6 Domain ..................................144.2.2. Mobility from a Non-PMIPv6 Domain to a
PMIPv6 Domain ......................................154.3. Solutions Related to Scenario B ...........................155. Security Considerations ........................................166. Contributors ...................................................167. Acknowledgements ...............................................168. References .....................................................178.1. Normative References ......................................178.2. Informative References ....................................171. Introduction
Proxy Mobile IPv6 (PMIPv6) [RFC5213] is a network-based IP mobility
protocol standardized by the IETF. In some deployment scenarios,
this protocol will be deployed together with Mobile IPv6 (MIPv6)
[RFC6275], for example, with PMIPv6 as local mobility protocol and
MIPv6 as global mobility protocol. While the usage of a local
mobility protocol should not have implications on how global mobility
is managed, since PMIPv6 is partially based on MIPv6 signaling and
data structure, some considerations are needed to understand how the
protocols interact and how the different scenarios can be enabled.

Some standardization fora are also investigating more complex
scenarios where the mobility of some nodes is handled using Proxy
Mobile IPv6, while other nodes use Mobile IPv6; or the mobility of a
node is managed in turn by a host-based and a network-based
mechanism. This also needs to be analyzed as a possible deployment
scenario.
This document provides a taxonomy of the most common scenarios that
require direct interaction between MIPv6 and PMIPv6. The list is not
meant to be exhaustive. Moreover, this document presents and
identifies most of the issues pertaining to these scenarios and
discusses possible means and mechanisms that are recommended to
enable them.
2. Terminology
General mobility terminology can be found in [RFC3753]. The
following acronyms are used in this document:
o AR (Access Router): first hop router
o BCE (Binding Cache Entry): an entry of the MIPv6 or PMIPv6 binding
cache
o LMA (Local Mobility Anchor): the PMIPv6 mobility anchor as
specified in [RFC5213]
o MAG (Mobility Access Gateway): the PMIPv6 client as specified in
[RFC5213]
o MN-HoA: the Home Address (HoA) of a Mobile Node (MN) in a PMIPv6
domain
o MN-HNP: the IPv6 prefix that is always present in the Router
Advertisements that the MN receives when it is attached to any of
the access links in that PMIPv6 domain (MN-HoA always belongs to
this prefix.)
o MIPv6-HoA: the HoA the MN includes in MIPv6 Binding Update
messages
o MIPv6-CoA: the Care-of Address the MN includes in MIPv6 Binding
Update messages

3. Overview of the Scenarios and Related Issues
Several scenarios can be identified where MIPv6 and PMIPv6 are
deployed in the same network. This document not only focuses on
scenarios where the two protocols are used by the same MN to manage
local and global mobility but also investigates more complex
scenarios where the protocols are more tightly integrated or where
there is a coexistence of nodes that do or do not implement MIPv6.
In particular, the scenario space can be split into hierarchical
deployments and alternative deployments of Mobile IP (MIP) and Proxy
Mobile IP (PMIP). Hierarchical deployments are scenarios where the
two mobility protocols are used in the same network in a hierarchical
manner for global and local mobility management. Alternative
deployments are scenarios where only one of the two protocols is used
for mobility management of a given MN.
The following hierarchical scenarios are identified:
Scenario A.1: In this scenario, PMIPv6 is used as a network-based
local mobility management protocol whereas MIPv6 is used as a global
mobility management protocol. This interaction is very similar to
the interaction between Hierarchical Mobile IPv6 (HMIPv6) and MIPv6
[RFC5380]; MIPv6 is used to manage mobility among different access
networks, while the mobility within the access network is handled by
PMIPv6. The address managed by PMIPv6 (i.e., the MN-HoA) is
registered as the Care-of Address by the MN at the Home Agent (HA).
This means that the HA has a BCE for MIPv6-HoA that points to the
MN-HoA.

The following figure illustrates this scenario.
+----+
| HA | MIPv6-HoA -> MN-HoA
+----+
/\
/ \
+-------------/----\--------------+
( / \ ) Global Mobile IPv6
( / \ ) Domain
+----------/----------\-----------+
/ \
+----+ +----+
MN-HoA -> MAG1 |LMA1| |LMA2|
+----+ +----+
//\\ \\
+----//--\\---+ +-----\\------+
( // \\ ) ( \\ ) Local Mobility Network
( // \\ ) ( \\ ) PMIPv6 domain
+-//--------\\+ +--------\\---+
// \\ \\
// \\ \\
// \\ \\
+----+ +----+ +----+
|MAG1| |MAG2| |MAG3|
+----+ +----+ +----+
| | |
[MN]
Figure 1: Scenario A.1
Scenario A.2: In this scenario, the MN is moving across different
access networks, some of them supporting PMIPv6 and some others not
supporting it. Therefore, the MN is roaming from an access network
where the mobility is managed through a network-based solution to an
access network where a host-based management (i.e., Mobile IPv6) is
needed. This scenario may have different sub-scenarios depending on
the relations between the MIPv6 home network and the PMIPv6 domain.
The following figure illustrates an example of this scenario, where
the MN is moving from an access network where PMIPv6 is supported
(i.e., MAG functionality is supported) to a network where PMIPv6 is
not supported (i.e., MAG functionality is not supported by the AR).
This implies that the home link of the MN is actually a PMIPv6
domain. In this case, the MIPv6-HoA is equal to the MN-HoA (i.e.,
the address managed by PMIPv6).

be a common mobility anchor that acts as MIPv6 Home Agent and PMIPv6
LMA, depending on the type of the node as depicted in the figure.
However, the LMA and HA can also be separated, and this has no impact
on the mobility of the nodes.
+--------+
| HA/LMA |
+--------+
+------+ +------+
| MAG1 | | MAG2 |
+------+ +------+
+-----------+
| IPv6 host | ----------------->
+-----------+ movement
+----------+
| MIPv6 MN | ----------------->
+----------+ movement
Figure 4: Scenario B
Note that some of the scenarios can be combined. For instance,
Scenario B can be combined with Scenario A.1 or Scenario A.2.
The following sections describe some possible issues for each
scenario. Respective recommendations are described in Section 4.3.
The specifications considered as a baseline for the analysis are the
following: [RFC6275], [RFC4877], and [RFC5213].
3.1. Issues Related to Scenario A.1
This scenario is very similar to other hierarchical mobility schemes,
including an HMIPv6-MIPv6 scheme. No issues have been identified in
this scenario. Note that a race condition where the MN registers the
CoA at the HA before the CoA is actually bound to the MAG at the LMA
is not possible. The reason is that per the PMIPv6 specification
[RFC5213], the MAG does not forward any packets sent by the MN until
the PMIPv6 tunnel is up, regardless the mechanism used for address
allocation.
Section 4.1 describes one message flow in case PMIPv6 is used as a
local mobility protocol and MIPv6 is used as a global mobility
protocol.
3.2. Issues Related to Scenario A.2
This section highlights some considerations that are applicable to
scenario A.2.

1. HoA management and lookup key in the binding cache
* In MIPv6 [RFC6275], the lookup key in the binding cache is the
HoA of the MN. In particular, the base specification
[RFC6275] doesn't require the MN to include any identifier,
such as the MN-ID [RFC4283], in the Binding Update message
other than its HoA. As described in [RFC4877], the identifier
of the MN is known by the Home Agent after the Internet Key
Exchange Protocol (IKEv2) exchange, but this is not used in
the MIPv6 signaling or as a lookup key for the binding cache.
On the other hand, as specified in [RFC5213], a Proxy Binding
Update contains the home prefix of the MN, the MN-ID and does
not include the HoA of the MN (since it may not be known by
the MAG and consequently by the HA/LMA). The lookup key in
the binding cache of the LMA is either the home prefix or the
MN-ID. This implies that lookup keys for MIPv6 and PMIPv6
registrations are different. Because of that, when the MN
moves from its home network (i.e., from the PMIPv6 domain) to
the foreign link, the Binding Update sent by the MN is not
identified by the HA as an update of the Proxy BCE containing
the home prefix of the MN, but a new binding cache entry is
created. Therefore, PMIPv6 and MIPv6 will always create two
different BCEs in the HA/LMA, which implies that the HA and
LMA are logically separated. How to handle the presence of
the two BCEs for the same MN is described in Section 4.2.
2. MIPv6 de-registration Binding Update deletes PMIPv6 binding cache
entry
* When the MN moves from a MIPv6 foreign network to the PMIPv6
home domain, the MAG registers the MN at the LMA by sending a
Proxy Binding Update. Subsequently, the LMA updates the MN's
BCE with the MAG address and the MAG emulates the MN's home
link. Upon detection of the home link, the MN will send a
de-registration Binding Update to its home agent. It is
necessary to make sure that the de-registration of the MIPv6
Binding Update does not change the PMIPv6 BCE just created by
the MAG.
3. Race condition between Binding Update and Proxy Binding Update
messages (Sequence Numbers and Timestamps)
* MIPv6 and PMIPv6 use different mechanisms for handling
re-ordering of registration messages and they are sent by
different entities. In MIPv6, Binding Update messages that
are sent by the MN to the home agent are ordered by the
sequence numbers. The other side, in PMIPv6, Proxy Binding
Update messages that are sent by the MAG to the LMA are

ordered by a timestamp option. When the MN moves from one
access where Mobile IP is used to another access when Proxy
Mobile IP is used, delay in the mobility signaling sent may
imply adverse situations. For example, if the MN sends a
Mobile IP Binding Update from access A before moving to access
B and this Binding Update gets delayed (e.g., a refresh
Binding Update), the Binding Update may reach the combined
LMA/HA after the Proxy Binding Update sent by the MAG,
re-directing packets to access A even after the MN has moved
to access B.
4. Threat of compromised MAG
* In the MIPv6 base specification [RFC6275], there is a strong
binding between the HoA registered by the MN and the Security
Association (SA) used to modify the corresponding BCE.
* In the PMIPv6 specification [RFC5213], the MAG sends Proxy
Binding Updates on behalf of a MN to update the BCE that
corresponds to the MN's HoA. Since the MAG sends the Binding
Updates, PMIPv6 requires SAs between each MAG and the LMA.
* As described in [RFC4832], in PMIPv6, MAG compromise or
impersonation is an issue. [RFC4832], Section 2.2, describes
how a compromised MAG can harm the functionality of an LMA,
e.g., manipulating the LMA's routing table (or binding cache).
* In this mixed scenario, both host-based and network-based SAs
are used to update the same binding cache entry at the HA/LMA
(but see the first bullet of this list, as the entry may not
be the same). Based on this consideration, the threat
described in [RFC4832] is worse as it also affects hosts that
are using the LMA/HA as MIPv6 HA and not using PMIPv6.
3.3. Issues Related to Scenario B
In this scenario, there are two types of nodes in the access network:
some nodes support MIPv6 while some others do not. The rationale
behind such a scenario is that the nodes implementing MIPv6 manage
their own mobility to achieve better performance, e.g., for inter-
technology handovers. Obviously, nodes that do not implement MIPv6
must rely on the network to manage their mobility; therefore, Proxy
MIPv6 is used for those nodes.
Based on the current PMIPv6 solution described in [RFC5213], in any
link of the PMIPv6 domain, the MAG emulates the MN's home link,
advertising the home link prefix to the MN in a unicast Router
Advertisement message. This ensures that the IP address of the MN is

still considered valid by the MN itself. The home network prefix
(and any other information needed to emulate the home link) is
included in the MN's profile that is obtained by the MAG via context
transfer or via a policy store.
However, in case there are nodes that implement MIPv6 and want to use
this protocol, the network must offer MIPv6 service to them. In such
a case, the MAG should not emulate the home link. Instead of
advertising the MN-HNP, the MAG should advertise the topologically
correct local IP prefix, i.e., the prefix belonging to the MAG, so
that the MN detects an IP movement, configures a new CoA, and sends a
MIPv6 Binding Update based on [RFC6275].
4. Analysis of Possible Solutions
4.1. Solutions Related to Scenario A.1
As mentioned in Section 3.1, there are no significant issues in this
scenario.
Figures 5 and 6 show a scenario where an MN is moving from one PMIPv6
domain to another, based on the scenario of Figure 1. In Figure 5,
the MN moves from an old MAG to MAG2 in the same PMIPv6 domain: this
movement triggers a PBU to LMA1 and the updating of the binding cache
at the LMA1. There is no MIPv6 signaling as the CoA_1 registered at
the HA is the HoA for the PMIPv6 session. In Figure 6, the MN moves
from MAG2 in the LMA1 PMIPv6 domain to MAG3 in a different PMIPv6
domain: this triggers the PMIPv6 signaling and the creation of a
binding at the LMA2. On the other hand, the local address of the
mobile node is changed, as the LMA has changed; therefore, the MN
sends a MIPv6 Binding Update to the HA with the new CoA_2.

4.2. Solutions Related to Scenario A.2
As described in Section 3.2, in this scenario, the MN relies on
PMIPv6 as long as it is in the PMIPv6 domain. The MN then uses MIPv6
whenever it moves out of the PMIPv6 domain, which basically implies
that the MIPv6 home link is a PMIPv6 domain.
Analyzing the issues described in Section 3.2, it is clear that most
of them are applicable only to the case where there is a common BCE
for the PMIPv6 registration and the MIPv6 registration. Issue 1, on
how the two protocols identify the BCE, is valid only in the case in
which we assume that a PMIPv6 message has any value for a MIPv6 BCE.
Also, Issues 2 and 3 are not applicable in the case in which
different logical BCEs are used by the LMA and the HA. For this
reason, it is recommended that when the MIPv6 home link is
implemented as a PMIPv6 domain, the HA/LMA implementation treat the
two protocols as independent.
In more detail, the following principles should be followed by the
HA/LMA implementation:
o PMIPv6 signaling does not overwrite any MIPv6 BCE. In particular,
when a PMIPv6 BCE is created for an MN that has previously created
a MIPv6 BCE, the MIPv6 BCE of the MN is not overwritten, and a new
PMIPv6 BCE is created.
o The downlink packets in the case where both the MIPv6 BCE and
PMIPv6 BCE exist are processed as follows:
1. The MIPv6 BCE is processed first. If the destination address
of the received downlink packet matches the BCE of the HA, the
packet is forwarded by encapsulating it with the CoA contained
in the BCE.
2. If the destination address does not match the MIPv6 BCE, the
BCE created by PMIPv6 is applied, and the packets are
encapsulated to the registered MAG.
The following subsections provide a description of the procedures
that will be followed by the MN and HA/LMA based on the above
principles. The analysis is performed in two different subsections,
depending on whether the MN moves from a PMIPv6 domain to a non-
PMIPv6 domain or vice versa.

4.2.1. Mobility from a PMIPv6 Domain to a Non-PMIPv6 Domain
Let's assume the MN is attached to a PMIPv6 domain and there is a
valid Proxy BCE at the LMA. Then, the MN moves to a different access
network and starts using MIPv6 (e.g., because PMIPv6 is not
supported). The MN needs to bootstrap MIPv6 parameters and send a
MIPv6 Binding Update in order to have service continuity. Therefore,
the following steps must be performed by the User Equipment (UE):
o HA/LMA address discovery: the MN needs to discover the IP address
of the LMA that has a valid BCE for its home network prefix. This
is described in Section 3.2 as Issue 4.
o SA establishment: the MN needs to establish an IPsec Security
Association with the HA/LMA as described in [RFC4877].
o HoA or home network prefix assignment: as part of the MIPv6
bootstrapping procedure, the HA assigns a MIPv6 HoA to the MN.
This address must be the same the MN was using in the PMIPv6
domain.
Since all these steps must be performed by the MN before sending the
Binding Update, they have an impact on the handover latency
experienced by the MN. For this reason, it is recommended that the
MN establish the IPsec SA (and, consequently, be provided by the HA/
LMA with a MIPv6-HoA) when it is initialized. This implies that the
MN has MIPv6 stack active while in the PMIPv6 domain, but as long as
it is attached to the same PMIPv6 domain, it will appear to the MN as
if it is attached to the home link.
In order to establish the SA with the HA/LMA, the MN needs to
discover the IP address of the LMA/HA while in the PMIPv6 domain.
This can be done either based on DNS or based on DHCPv6, as described
in [RFC5026] and [RFC6611]. The network should be configured so that
the MN discovers or gets assigned the same HA/LMA that was serving as
the LMA in the PMIPv6 domain. Details of the exact procedure are out
of scope of this document.
When the MN establishes the SA, it acquires an HoA based on
[RFC5026]. However, based on PMIPv6 operations, the LMA knows only
the home network prefix used by the MN and does not know the MN-HoA.
For this reason, the MN must be configured to propose the MN-HoA as
the HoA in the IKEv2 INTERNAL_IP6_ADDRESS attribute during the IKEv2
exchange with the HA/LMA. Alternatively, the HA/LMA can be
configured to provide the entire home network prefix via the
MIP6_HOME_LINK attribute to the MN as specified in [RFC5026]; based
on this home network prefix, the MN can configure an HoA. Note that
the SA must be bound to the MN-HoA used in the PMIPv6 domain as per

[RFC4877]. Note that the home network prefix is shared between the
LMA and HA, and this implies that there is an interaction between the
LMA and the HA in order to assign a common home network prefix when
triggered by PMIPv6 and MIPv6 signaling.
When the MN hands over to an access network that does not support
Proxy Mobile IPv6, it sends a Binding Update to the HA. The MN may
set the R bit defined in the Network Mobility (NEMO) specification
(implicit mode) [RFC3963] in order to indicate that the entire HNP is
moved to the new CoA. A MIPv6 BCE is created irrespective of the
existing PMIPv6 BCE. Packets matching the MIPv6 BCE are sent to the
CoA present in the MIPv6 BCE. The PMIPv6 BCE will expire in the case
in which the MAG does not send a refresh PBU.
4.2.2. Mobility from a Non-PMIPv6 Domain to a PMIPv6 Domain
In this section, it is assumed that the MN is in a non-PMIPv6 access
network, and it has bootstrapped MIPv6 operations based on [RFC5026];
therefore, there is valid binding cache for its MIPv6-HoA (or HNP in
case of NEMO) at the HA. Then, the MN moves to a PMIPv6 domain that
is configured to be the home link for the MIPv6-HoA the MN has been
assigned.
In order to provide session continuity, the MAG needs to send a PBU
to the HA/LMA that was serving the MN. The MAG needs to discover the
HA/LMA; however, [RFC5213] assumes that the LMA is assigned to the
MAG or discovered by the MAG when the MN attaches to the MAG. The
exact mechanism is not specified in [RFC5213]. A detailed
description of the necessary procedure is out of the scope of this
document. Note that the MAG may also rely on static configuration or
lower-layer information provided by the MN in order to select the
correct HA/LMA.
The PBU sent by the MAG creates a PMIPv6 BCE for the MN that is
independent of the MIPv6 BCE. Traffic destined to the MIPv6-HoA (or
to the HNP in case the MN had set the flag R in the last BU) is still
forwarded to the CoA present in the MIPv6 BCE. When the MN wants to
use the HoA directly from the home link, it sends a de-registration
message and, at that point only, the PMIPv6 BCE is present.
4.3. Solutions Related to Scenario B
The solution for this scenario depends on the access network being
able to determine that a particular MN wants to use Mobile IPv6.
This requires a solution at the system level for the access network
and may require knowledge of the detailed configuration and software
capabilities of every MN in the system. These issues are out of the
scope of this document.

5. Security Considerations
Scenario A.1 does not introduce any new security issues in addition
to those described in [RFC5213] or [RFC6275].
For Scenario A.2, this document requires that the a home agent that
also implements the PMIPv6 LMA functionality should allow both the MN
and the authorized MAGs to modify the BCEs for the MN. Note that the
compromised MAG threat described in [RFC4832] also applies here in a
more severe form as explained in Section 3.2. Scenario B relies on
the secure identification of MNs and their capabilities so that the
right service can be provided for the right MNs. For instance, a
malicious MN should not get the HoA of some other node assigned to
it, and a MN that desires to employ its own mobility management
should be able to do so. The ability to identify nodes is already a
requirement in [RFC5213], but Scenario B adds a requirement on
identification of node capabilities.
6. Contributors
Kuntal Chowdhury - kuntal@hotmail.com
Vijay Devarapalli - vijay.devarapalli@azairenet.com
Sri Gundavelli - sgundave@cisco.com
Suresh Krishnan - suresh.krishnan@ericsson.com
Ahmad Muhanna - amuhanna@nortel.com
Hesham Soliman - Hesham@elevatemobile.com
George Tsirtsis - tsirtsis@googlemail.com
Genadi Velev - Genadi.Velev@eu.panasonic.com
Kilian Weniger - Kilian.Weniger@googlemail.com
7. Acknowledgements
This document is a merge of four different documents: "Proxy Mobile
IPv6 and Mobile IPv6 interworking issues" (April 2007), "Proxy Mobile
IPv6 and Mobile IPv6 interworking" (April 2007), "Behavior of
Collocated HA/LMA" (October 2008), and "Interactions between PMIPv6
and MIPv6: scenarios and related issues" (November 2007). Thanks to
the authors and editors of those documents.